In recent years, it has been said that owing to the influence of chemical treatment caused by, for example, hair coloring or physical treatment caused by blowing, cuticles on the hair surface peel off or the hair becomes porous by the efflux of lipids from the inside of the hair and as a result, the hair becomes excessively dry, resistant to finger combing, unmanageable and lusterless.
Leave-on hair cosmetic compositions mainly used now include emulsion type products such as hair cream containing wax, higher alcohol and surfactant to provide the hair with manageability and protect the hair from excessive dryness; and gel type products containing a film forming polymer (set polymer). Such hair cosmetic compositions can temporarily solve the problems such as poor manageability and excessive dryness by causing an oil or fat or polymer to adhere to the hair surface, but cannot fundamentally improve the hair luster or manageability.
Some hair cosmetic compositions for improving the hair quality are known and compositions using a specific organic acid and organic solvent, on which an attempt was made to improve the hair quality by acting on the inside of the hair, are known. Of these, leave-on hair cosmetic compositions containing both malic acid and lactic acid as the organic acid and further containing an organic solvent are proposed (refer to Patent Document 1). Continuous use of this hair cosmetic composition can gradually improve the hair luster and especially improve the set retention property under high humidity, manageability, and hair feel. Such a hair cosmetic composition is disclosed also in Patent Documents 2 and 3.
The hair cosmetic composition disclosed in Patent Document 1 has good affinity to either wet hair or dry hair when the composition is applied thereto, but it does not enable sufficient smooth finger combing. In addition, even after continuous use, it does not have a sufficient effect of improving manageability, particularly under high humidity. The hair cosmetic composition disclosed in Patent Document 2 or 3, on the other hand, does not have a satisfactory effect on affinity and finger combability when applied to dry hair or wet hair (especially, dry hair). In addition, continuous use thereof does not have a satisfactory effect of improving manageability/finger combability or improving manageability under high humidity.    [Patent Document 1] JP-A-2004-189727    [Patent Document 2] JP-A-2007-186474 (Example 10)    [Patent Document 3] JP-A-2006-290796 (Example 6 and Example 8)